Systems and methods for radiometrically measuring temperature during tissue ablation

ABSTRACT

The present invention provides systems and methods for radiometrically measuring temperature during ablation. An interface module includes a processor; a first input/output (I/O) port configured to receive digital radiometer and thermocouple signals from an integrated catheter tip (ICT) that includes a radiometer; a second I/O port configured to receive ablative energy from an electrosurgical generator; a temperature display; a patient relay in communication with the first and second I/O ports and the processor; and a computer-readable medium storing radiometer and thermocouple operation parameters and instructions for causing the processor to: calculate a temperature adjacent to the ICT based on the radiometer and thermocouple signals and the operation parameters, causing the temperature display to display the calculated temperature, and closing the patient relay so as to pass ablative energy received on the second I/O port to the first I/O port.

FIELD OF THE INVENTION

This application generally relates to systems and methods for measuringtemperature during tissue ablation.

BACKGROUND OF THE INVENTION

Tissue ablation may be used to treat a variety of clinical disorders.For example, tissue ablation may be used to treat cardiac arrhythmias bydestroying aberrant pathways that would otherwise conduct abnormalelectrical signals to the heart muscle. Several ablation techniques havebeen developed, including cryoablation, microwave ablation, radiofrequency (RF) ablation, and high frequency ultrasound ablation. Forcardiac applications, such techniques are typically performed by aclinician who introduces a catheter having an ablative tip to theendocardium via the venous vasculature, positions the ablative tipadjacent to what the clinician believes to be an appropriate region ofthe endocardium based on tactile feedback, mapping electrocardiogram(ECG) signals, anatomy, and/or fluoroscopic imaging, actuates flow of anirrigant to cool the surface of the selected region, and then actuatesthe ablative tip for a period of time believed sufficient to destroytissue in the selected region.

Although commercially available ablative tips may include thermocouplesfor providing temperature feedback via a digital display, suchthermocouples typically do not provide meaningful temperature feedbackduring irrigated ablation. For example, the thermocouple only measuressurface temperature, whereas the heating or cooling of the tissue thatresults in tissue ablation may occur at some depth below the tissuesurface. Moreover, for procedures in which the surface of the tissue iscooled with an irrigant, the thermocouple will measure the temperatureof the irrigant, thus further obscuring any useful information about thetemperature of the tissue, particularly at depth. As such, the clinicianhas no useful feedback regarding the temperature of the tissue as it isbeing ablated or whether the time period of the ablation is sufficient.

Accordingly, it may only be revealed after the procedure iscompleted—for example, if the patient continues to experience cardiacarrhythmias—that the targeted aberrant pathway was not adequatelyinterrupted. In such a circumstance, the clinician may not know whetherthe procedure failed because the incorrect region of tissue was ablated,because the ablative tip was not actuated for a sufficient period oftime to destroy the aberrant pathway, because the ablative tip was nottouching or insufficiently touching the tissue, because the power of theablative energy was insufficient, or some combination of the above. Uponrepeating the ablation procedure so as to again attempt to treat thearrhythmia, the clinician may have as little feedback as during thefirst procedure, and thus potentially may again fail to destroy theaberrant pathway. Additionally, there may be some risk that theclinician would re-treat a previously ablated region of the endocardiumand not only ablate the conduction pathway, but damage adjacent tissues.

In some circumstances, to avoid having to repeat the ablation procedureas such, the clinician may ablate a series of regions of the endocardiumalong which the aberrant pathway is believed to lie, so as to improvethe chance of interrupting conduction along that pathway. However, thereis again insufficient feedback to assist the clinician in determiningwhether any of those ablated regions are sufficiently destroyed.

U.S. Pat. No. 4,190,053 to Sterzer describes a hyperthermia treatmentapparatus in which a microwave source is used to deposit energy inliving tissue to effect hyperthermia. The apparatus includes aradiometer for measuring temperature at depth within the tissue, andincludes a controller that feeds back a control signal from theradiometer, corresponding to the measured temperature, to control theapplication of energy from the microwave source. The apparatusalternates between delivering microwave energy from the microwave sourceand measuring the radiant energy with the radiometer to measure thetemperature. As a consequence of this time division multiplexing ofenergy application and temperature measurement, temperature valuesreported by the radiometer are not simultaneous with energy delivery.

U.S. Pat. No. 7,769,469 to Carr et al. describes an integrated heatingand sensing catheter apparatus for treating arrhythmias, tumors andlike, having a diplexer that permits near simultaneous heating andtemperature measurement. This patent too describes that temperaturemeasured by the radiometer may be used to control the application ofenergy, e.g., to maintain a selected heating profile.

Despite the promise of precise temperature measurement sensitivity andcontrol offered by the use of radiometry, there have been few successfulcommercial medical applications of this technology. One drawback ofpreviously-known systems has been an inability to obtain highlyreproducible results due to slight variations in the construction of themicrowave antenna used in the radiometer, which can lead to significantdifferences in measured temperature from one catheter to another.Problems also have arisen with respect to orienting the radiometerantenna on the catheter to adequately capture the radiant energy emittedby the tissue, and with respect to shielding high frequency microwavecomponents in the surgical environment so as to prevent interferencebetween the radiometer components and other devices in the surgicalfield.

Acceptance of microwave-based hyperthermia treatments and temperaturemeasurement techniques also has been impeded by the capital costsassociated with implementing radiometric temperature control schemes.Radiofrequency ablation techniques have developed a substantialfollowing in the medical community, even though such systems can havesevere limitations, such as the inability to accurately measure tissuetemperature at depth, e.g., where irrigation is employed. However, thewidespread acceptance of RF ablation systems, extensive knowledge baseof the medical community with such systems, and the significant costrequired to changeover to, and train for, newer technologies hasdramatically retarded the widespread adoption of radiometry.

In view of the foregoing, it would be desirable to provide apparatus andmethods that permit radiometric measurement of temperature at depth intissue, and permit use of such measurements to control the applicationof energy in a hyperthermia treatment.

It further would be desirable to provide apparatus and methods thatemploy microwave radiometer components that can be readily constructedand calibrated to provide a high degree of measurement reproducibilityand reliability.

It also would be desirable to provide apparatus and methods that permitradiometric temperature measurement and control techniques to beintroduced in a manner that is readily accessible to clinicians trainedin the use of previously-known RF ablation catheters, with a minimum ofretraining.

It still further would be desirable to provide apparatus and methodsthat permit radiometric temperature measurement and control techniquesto be readily employed with previously-known RF electrosurgicalgenerators, thereby reducing the capital costs needed to implement suchnew techniques.

SUMMARY OF THE INVENTION

In view of the foregoing, it would be desirable to provide apparatus andmethods for treating living tissue that employs a radiometer fortemperature measurement and control. In accordance with one aspect ofthe invention, systems and methods are provided for radiometricallymeasuring temperature during RF ablation, i.e., calculating temperaturebased on signal(s) from a radiometer. Unlike standard thermocoupletechniques used in existing commercial ablation systems, a radiometermay provide useful information about tissue temperature at depth—wherethe tissue ablation occurs—and thus provide feedback to the clinicianabout the extent of tissue damage as the clinician ablates a selectedregion of the heart muscle.

In one embodiment, the present invention comprises an interface module(system) that may be coupled to a previously-known commerciallyavailable ablation energy generator, e.g., an electrosurgical generator,thereby enabling radiometric techniques to be employed with reducedcapital outlay. In this manner, the conventional electrosurgicalgenerator can be used to supply ablative energy to an “integratedcatheter tip” (ICT) that includes an ablative tip, a thermocouple, and aradiometer for detecting the volumetric temperature of tissue subjectedto ablation. The interface module is configured to be coupled betweenthe conventional electrosurgical generator and the ICT, and tocoordinate signals therebetween. The interface module thereby providesthe electrosurgical generator with the information required foroperation, transmits ablative energy to the ICT under the control of theclinician, and displays via a temperature display the temperature atdepth of tissue as it is being ablated, for use by the clinician. Thedisplayed temperature may be calculated based on signal(s) measured bythe radiometer using algorithms such as discussed further below.

In an exemplary embodiment, the interface module includes a firstinput/output (I/O) port that is configured to receive a digitalradiometer signal and a digital thermocouple signal from the ICT, and asecond I/O port that is configured to receive ablative energy from theelectrosurgical generator. The interface module also includes aprocessor, a patient relay in communication with the processor and thefirst and second I/O ports, and a persistent computer-readable medium.The computer-readable medium stores operation parameters for theradiometer and the thermocouple, as well as instructions for theprocessor to use in coordinating operation of the ICT and theelectrosurgical generator.

The computer-readable medium preferably stores instructions that causethe processor to execute the step of calculating a temperature adjacentto the ICT based on the digital radiometer signal, the digitalthermocouple signal, and the operation parameters. This temperature isexpected to provide significantly more accurate information about lesionquality and temperature at depth in the tissue than would a temperaturebased solely on a thermocouple readout. The computer-readable medium mayfurther store instructions for causing the processor to cause thetemperature display to display the calculated temperature, for exampleso that the clinician may control the time period for ablationresponsive to the displayed temperature. The computer-readable mediummay further store instructions for causing the processor to close thepatient relay, such that the patient relay passes ablative energyreceived on the second I/O port, from the electrosurgical generator, tothe first I/O port, to the ICT. Note that the instructions may cause theprocessor to maintain the patient relay in a normally closed state, andto open the patient relay upon detection of unsafe conditions.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a schematic illustration of a first embodiment of anarrangement including an interface module according to one aspect of thepresent invention, including a display of the front and back panels of,and exemplary connections between, the interface module, a previouslyknown ablation energy generator, e.g., electrosurgical generator, and anintegrated catheter tip (ICT).

FIG. 1B is a schematic illustrating exemplary connections to and fromthe interface module of FIG. 1A, as well as connections among othercomponents that may be used with the interface module.

FIG. 2A is a schematic illustrating internal components of the interfacemodule of FIGS. 1A-1B.

FIG. 2B schematically illustrates additional internal components of theinterface module of FIG. 2A, as well as selected connections to and fromthe interface module.

FIG. 3A illustrates steps in a method of using the interface module ofFIGS. 1A-2B during tissue ablation.

FIG. 3B illustrates steps in a method of calculating radiometrictemperature using digital signals from a radiometer and a thermocoupleand operation parameters.

FIG. 3C illustrates steps in a method of controlling an ablationprocedure using a temperature calculated based on signal(s) from aradiometer using the interface module of FIGS. 1A-2B.

FIGS. 4A-4D illustrate data obtained during exemplary ablationprocedures performed using the interface module of FIGS. 1A-2B.

FIG. 5A illustrates a plan view of an exemplary patient interface module(PIM) associated with an integrated catheter tip (ICT) for use with theinterface module of FIGS. 1A-2B.

FIG. 5B schematically illustrates selected internal components of thePIM of FIG. 5A, according to some embodiments of the present invention.

FIGS. 6A-6B respectively illustrate perspective and exploded views of anexemplary integrated catheter tip (ICT) for use with the interfacemodule of FIGS. 1A-2B and the PIM of FIGS. 5A-5B, according to someembodiments of the present invention.

DETAILED DESCRIPTION

Embodiments of the present invention provide systems and methods forradiometrically measuring temperature during ablation, in particularcardiac ablation. As noted above, commercially available systems forcardiac ablation may include thermocouples for measuring temperature,but such thermocouples may not adequately provide the clinician withinformation about tissue temperature. Thus, the clinician may need tomake an “educated guess” about whether a given region of tissue has beensufficiently ablated to achieve the desired effect. By comparison,calculating a temperature based on signal(s) from a radiometer isexpected to provide accurate information about the temperature of tissueat depth, even during an irrigated procedure. The present inventionprovides a “retrofit” solution that includes an interface module thatworks with existing, commercially available ablation energy generators,such as electrosurgical generators. In accordance with one aspect of thepresent invention, the interface module displays a tissue temperaturebased on signal(s) measured by a radiometer, that a clinician may use toperform ablation procedures with significantly better accuracy than canbe achieved using only a thermocouple for temperature measurement.

First, high level overviews of the interface module and connectionsthereto are provided. Then, further detail on the internal components ofthe interface module, and exemplary methods of calculating radiometrictemperature and controlling an ablation procedure based on same, areprovided. Data obtained during experimental procedures also ispresented. Lastly, further detail on components that may be used withthe interface module is provided.

FIG. 1A illustrates plan views of front panel 111, back panel 112, andconnections to and from exemplary interface module 110, constructed inaccordance with the principles of the present invention. As illustrated,front panel 111 of interface module 110 may be connected to a catheter120 that includes patient interface module (PIM) 121 and integratedcatheter tip (ICT) 122. Catheter 120 optionally is steerable, or may benon-steerable and used in conjunction with a robotic positioning systemor a third-party steerable sheath (not shown). ICT 122 is positioned bya clinician (optionally with mechanical assistance such as noted above),during a procedure, within subject 101 lying on grounded table 102. ICT122 may include, among other things, an ablative tip, a thermocouple,and a radiometer for detecting the volumetric temperature of tissuesubjected to ablation. The ICT 122 optionally includes one or moreirrigation ports, which in one embodiment may be connected directly to acommercially available irrigant pump.

In embodiments in which the ablation energy is radiofrequency (RF)energy, the ablative tip may include an irrigated ablation electrode,such as described in greater detail below with reference to FIGS. 6A-6B.ICT 122 further may include one or more electrocardiogram (ECG)electrodes for use in monitoring electrical activity of the heart ofsubject 101. Interface module 110 receives signals from thethermocouple, radiometer, and optional ECG electrodes of ICT 122 via PIM121. Interface module 110 provides to ICT 122, via PIM 121, power forthe operation of the PIM and the sensors (thermocouple, radiometer, andECG electrodes), and ablation energy to be applied to subject 101 viathe ablative tip.

Back panel 112 of interface module 110 may be connected via connectioncable 135 to a commercially available previously-known ablation energygenerator 130, for example an electrosurgical generator 130, such as aStockert EP-Shuttle 100 Generator (Stockert GmbH, Freiburg Germany) orStockert 70 RF Generator (Biosense Webster, Diamond Bar, Calif.). Inembodiments where the electrosurgical generator 130 is a StockertEP-Shuttle or 70 RF Generator, generator 130 includes display device 131for displaying temperature and the impedance and time associated withapplication of a dose of RF ablation energy; power control knob 132 forallowing a clinician to adjust the power of RF ablative energy deliveredto subject 101; and start/stop/mode input for allowing a clinician toinitiate or terminate the delivery of RF ablation energy.Start/stop/mode input also may be configured to control the mode ofenergy delivery, e.g., whether the energy is to be cut off after a givenperiod of time.

Although generator 130 may be configured to display temperature ondisplay device 131, that temperature is based on readings from astandard thermocouple. As noted above, however, that reportedtemperature may be inaccurate while irrigant and ablative energy arebeing applied to tissue. Interface module 110 provides to generator 130,via connection cable 135, a thermocouple signal for use in displayingsuch a temperature, and signals from the ECG electrodes; and providesvia indifferent electrode cable 134 a pass-through connection toindifferent electrode 140. Interface module 110 receives from generator130, via connection cable 135, RF ablation energy that module 110controllably provides to ICT 122 for use in ablating tissue of subject101.

As will be familiar to those skilled in the art, for a monopolar RFablation procedure, a clinician may position an indifferent electrode(IE) on the back of subject 101 so as to provide a voltage differentialthat enables transmission of RF energy into the tissue of the subject.In the illustrated embodiment, the IE is connected to interface module110 via first indifferent electrode cable 141. Interface module 110passes through the IE signal to second indifferent electrode cable 134,which is connected to an indifferent electrode input port onelectrosurgical generator 130. Alternatively, the IE may be connecteddirectly to that port of the electrosurgical generator 130 viaappropriate cabling (not shown).

It should be understood that electrosurgical generators other than theStockert EP-Shuttle or 70 RF Generator suitably may be used, e.g., othermakes or models of RF electrosurgical generators. Alternatively,generators that produce other types of ablation energy, such asmicrowave generators, cryosurgical sources, or high frequency ultrasoundgenerators, may be used. Ablation energy generator 130 need notnecessarily be commercially available, although as noted above it may beconvenient to use one that is. It should also be appreciated that theconnections described herein may be provided on any desired face orpanel of interface module 110, and that the functionalities of differentconnectors and input/output (I/O) ports may be combined or otherwisesuitably modified.

Front panel 111 of interface module 110 includes temperature display113, e.g., a digital two or three-digit display device configured todisplay a temperature calculated by a processor internal to interfacemodule 110, e.g., as described in greater detail below with reference toFIGS. 2A-2B and 3A. Other types of temperature displays, such multicolorliquid crystal displays (LCDs), alternatively may be used. Front panel111 also includes connectors (not labeled) through which interfacemodule 110 is connected to ICT 122 via PIM 121, and to the IE 140 viaindifferent electrode cable 141.

Back panel 111 of interface module 110 includes connectors (not labeled)through which interface module 110 is connected to electrosurgicalgenerator 130, via indifferent electrode cable 134 and connection cable135. Back panel 112 of interface module 110 also includes data ports 114configured to output one or more signals to a suitably programmedpersonal computer or other remote device, for example an EPmonitoring/recording system such as the LABSYSTEM™ PRO EP RecordingSystem (C.R. Bard, Inc., Lowell, Mass.). Such signals may, for example,include signals generated by the thermocouple, radiometer, and/or ECGelectrodes of the ICT, the tissue temperature calculated by interfacemodule 110, and the like.

Referring now to FIG. 1B, exemplary connections to and from theinterface module of FIG. 1A, as well as connections among othercomponents, are described. In FIG. 1B, interface module 110 is inoperable communication with catheter 120 having a patient interfacemodule (PIM) 121 and an integrated catheter tip (ICT) 122 that includesa radiometer, ablative tip, a thermocouple (TC), and optionally alsoincludes ECG electrodes and/or irrigation ports(s). Interface module 110is also in operable communication with electrosurgical generator 130 andindifferent electrode 140.

Electrosurgical generator 130 optionally is in operable communicationwith electrophysiology (EP) monitoring/recording system 160 viaappropriate cabling. Alternatively, as illustrated in FIG. 1B, interfacesystem 110 may be directly connected to EP monitoring/recording module160 via appropriate cabling and data ports 114. EP monitoring/recordingsystems may include, for example, various monitors, processors, and thelike that display pertinent information about an ablation procedure to aclinician, such as the subject's heart rate and blood pressure, thetemperature recorded by the thermocouple on the catheter tip, theablation power and time period over which it is applied, fluoroscopicimages, and the like. EP monitoring/recording systems are commerciallyavailable, e.g., the MEDELEC™ Synergy T-EP—EMG/EP Monitoring System(CareFusion, San Diego, Calif.), or the LABSYSTEM™ PRO EP RecordingSystem (C.R. Bard, Inc., Lowell, Mass.).

If the ICT 122 includes irrigation port(s), then one convenient means ofproviding irrigant to such ports is irrigation pump 140 associated withelectrosurgical generator 130, which pump is in operable communicationwith the generator and in fluidic communication with the ICT. Forexample, the Stockert 70 RF Generator is designed for use with aCoolFlow™ Irrigation pump, also manufactured by Biosense Webster.Specifically, the Stockert 70 RF Generator and the CoolFlow™ pump may beconnected to one another by a commercially available interface cable, soas to operate as an integrated system that works in substantially thesame way as it would with a standard, commercially available cathetertip. For example, prior to positioning ICT 122 in the body, theclinician instructs the pump to provide a low flow rate of irrigant tothe ICT, as it would to a standard catheter tip; the ICT is thenpositioned in the body. Then, when the clinician presses the “start”button on the face of generator 130, the generator may instruct pump 150to provide a high flow rate of irrigant for a predetermined period(e.g., 5 seconds) before providing RF ablation energy, again as it wouldfor a standard catheter tip. After the RF ablation energy application isterminated, then pump 150 returns to a low flow rate after anotherpredetermined period (e.g., 5 seconds). The pump remains at a low flowrate until the clinician removes the ICT 122 from the body and manuallyturns off the pump.

Referring now to FIGS. 2A-2B, further details of internal components ofinterface module 110 of FIGS. 1A-1B are provided.

FIG. 2A schematically illustrates internal components of one embodimentof interface module 110. Interface module 110 includes first, second,third, and fourth ports 201-204 by which it communicates with externalcomponents. Specifically, first port 201 is an input/output (I/O) portconfigured to be connected to catheter 120 via PIM 121, as illustratedin FIG. 1A. Port 201 receives as input from catheter 120 digitalradiometer and digital thermocouple (TC) signals, and optionally ECGsignals, generated by ICT 122, and provides as output to catheter 120 RFablation energy, as well as power for circuitry within the ICT 122 andthe PIM 121. Second port 202 is also an I/O port, configured to beconnected to electrosurgical generator 130 via connection cable 135illustrated in FIG. 1A, and receives as input from generator 130 RFablation energy, and provides as output to generator 130 a reconstitutedanalog thermocouple (TC) signal and raw ECG signal(s). Third port 203 isan input port configured to be connected to indifferent electrode (IE)140 via indifferent electrode cable 134 illustrated in FIG. 1A, andfourth port 204 is an output port configured to be connected togenerator 130 via indifferent electrode cable 141 illustrated in FIG.1A. As shown in FIG. 2A, interface module 110 acts as a pass-through forthe IE signal from IE 140 to generator 130, and simply receives IEsignal on third port 203 and provides the IE signal to generator 130 onfourth port 204.

Interface module 110 also includes processor 210 coupled to non-volatile(persistent) computer-readable memory 230, user interface 280, loadrelay 260, and patient relay 250. Memory 230 stores programming thatcauses processor 210 to perform steps described further below withrespect to FIGS. 3A-3C, thereby controlling the functionality ofinterface module 110. Memory 230 also stores parameters used byprocessor 210. For example, memory 230 may store a set of operationparameters 231 for the thermocouple and radiometer, as well as atemperature calculation module 233, that processor 210 uses to calculatethe radiometric temperature based on the digital TC and radiometersignals received on first I/O port 201, as described in greater detailbelow with respect to FIG. 3B. The operation parameters 231 may beobtained through calibration, or may be fixed. Memory 230 also stores aset of safety parameters 232 that processor 210 uses to maintain safeconditions during an ablation procedure, as described further below withrespect to FIG. 3C. Memory 230 further stores decision module 234 thatprocessor 210 uses to control the opening and closing of patient relay250 and load relay 260 based on its determinations of temperature andsafety conditions, as described further below with reference to FIGS.3A-3C. When closed, patient relay 250 passes ablative energy from thesecond I/O port 202 to the first I/O port 201. When closed, load relay260 returns ablative energy to the IE 140 via dummy load D (resistor,e.g., of 120Ω resistance) and fourth I/O port 204.

As illustrated in FIG. 2A, interface module 110 further includes userinterface 280 by which a user may receive information about thetemperature adjacent ICT 122 as calculated by processor 210, as well asother potentially useful information. In the illustrated embodiment,user interface 280 includes digital temperature display 113, whichdisplays the instantaneous temperature calculated by processor 210. Inother embodiments (not shown), display 113 may be an LCD device that, inaddition to displaying the instantaneous temperature calculated byprocessor 210, also graphically display changes in the temperature overtime for use by the clinician during the ablation procedure. Userinterface 280 further may include data ports 114, which may be connectedto a computer or EP monitoring/recording system by appropriate cablingas noted above, and which may output digital or analog signals beingreceived or generated by interface module 110, e.g., radiometersignal(s), a thermocouple signal, and/or the temperature calculated byprocessor 210.

So as to inhibit potential degradations in the performance of processor210, memory 230, or user interface 280 resulting from electrical contactwith RF energy, interface module 110 may include opto-electronics 299that communicate information to and from processor 210, but thatsubstantially inhibit transmission of RF energy to processor 210, memory230, or user interface 280. This isolation is designated by the dashedline in FIG. 2A. For example, opto-electronics 299 may include circuitrythat is in operable communication with first I/O port 201 so as toreceive the digital TC and radiometer signals from first I/O port 201,and that converts such digital signals into optical digital signals.Opto-electronics 299 also may include an optical transmitter in operablecommunication with such circuitry, that transmits those optical digitalsignals to processor 210 through free space. Opto-electronics 299further may include an optical receiver in operable communication withprocessor 210, that receives such optical digital signals, and circuitrythat converts the optical digital signals into digital signals for useby processor 210. The opto-electronic circuitry in communication withthe processor also may be in operable communication with a secondoptical transmitter, and may receive signals from processor 210 to betransmitted across free space to an optical receiver in communicationwith the circuitry that receives and processes the digital TC andradiometer signals. For example, processor 210 may transmit to suchcircuitry, via an optical signal, a signal that causes the circuitry togenerate an analog version of the TC signal and to provide that analogsignal to the second I/O port. Because opto-electronic circuitry,transmitters, and receivers are known in the art, its specificcomponents are not illustrated in FIG. 2A.

With respect to FIG. 2B, additional internal components of interfacemodule 110 of FIG. 2A are described, as well as selected connections toand from the interface module. FIG. 2B is an exemplary schematic for agrounding and power supply scheme suitable for using interface module110 with an RF electrosurgical generator, e.g., a Stockert EP-Shuttle or70 RF Generator. Other grounding and power supply schemes suitably maybe used with other types, makes, or models of electrosurgicalgenerators, as will be appreciated by those skilled in the art.

As illustrated in FIG. 2B, interface module 110 includes isolated mainpower supply 205 that may be connected to standard three-prong A/C poweroutlet 1, which is grounded to mains ground G. Interface module 110 alsoincludes several internal grounds, designated A, B, C, and I. Internalground A is coupled to the external mains ground G via a relativelysmall capacitance capacitor (e.g., a 10 pF capacitor) and a relativelyhigh resistance resistor (e.g., a 20 MΩ resistor) that substantiallyprevents internal ground A from floating. Internal ground B is coupledto internal ground A via a low resistance pathway (e.g., a pathway orresistor(s) providing less than 1000Ω resistance, e.g., about 0Ωresistance). Similarly, internal ground C is coupled to internal groundB via another low resistance pathway. Internal ground I is an isolatedground that is coupled to internal ground C via a relatively smallcapacitance capacitor (e.g., a 10 pF capacitor) and a relatively highresistance resistor (e.g., a 20 MΩ resistor) that substantially preventsisolated ground I from floating.

Isolated main power supply 205 is coupled to internal ground A via a lowresistance pathway. Isolated main power supply 205 is also coupled to,and provides power (e.g., ±12V) to, one or more internal isolated powersupplies that in turn provide power to components internal to interfacemodule 110. Such components include, but are not limited to componentsillustrated in FIG. 2A. For example, interface module 110 may includeone or more isolated power supplies 220 that provide power (e.g., ±4V)to processor 210, memory 230, and analog circuitry 240. Analog circuitry240 may include components of user interface 280, including temperaturedisplay 113 and circuitry that appropriately prepares signals for outputon data ports 114. Data ports 114, as well as analog circuitry 240, arecoupled to internal ground B via low resistance pathways, whileprocessor and memory 210, 230 are coupled to internal ground C via lowresistance pathways. Interface module also may include one or moreisolated power supplies 270 that provide power (e.g., ±4V) to ICT 122,PIM 121, and RF circuitry 290.

RF circuitry 290 may include patient and load relays 250, 260, as wellas circuitry that receives the radiometer and thermocouple signals andprovides such signals to the processor via optoelectronic coupling, andcircuitry that generates a clock signal to be provided to the ICT asdescribed further below with reference to FIG. 5B. RF circuitry 290, ICT122, and PIM 121 are coupled to isolated internal ground I via lowresistance pathways.

As shown in FIG. 2B, power supply 139 of RF electrosurgical generator130, which may be external to generator 130 as in FIG. 2B or may beinternal to generator 130, is connected to standard two- or three-prongA/C power outlet 2. However, generator power supply 139 is not connectedto the ground of the outlet, and thus not connected to the mains groundG, as is the isolated main power supply. Instead, generator power supply139 and RF electrosurgical generator 130 are grounded to internalisolated ground I of interface module 110 via low resistance pathwaysbetween generator 130 and PIM 121 and ICT 122, and low resistancepathways between PIM 121 and ICT 122 and internal isolated ground I. Assuch, RF circuitry 290, PIM 121, IE 140, and generator 130 are all“grounded” to an internal isolated ground I that has essentially thesame potential as does ICT 122. Thus, when RF energy is applied to ICT122 from generator 130 through interface module 110, the ground of RFcircuitry 290, PIM 121, ICT 122, IE 140, and generator 130 allessentially float with the RF energy amplitude, which may be a sine waveof 50-100V at 500 kHz.

As further illustrated in FIG. 2B, the ±12V of power that isolated mainpower supply 205 provides to isolated processor/memory/analog powersupply 220 and to isolated ICT/RF power supply 270 may be coupled byparasitic capacitance (pc, approximately 13 pF) to A/C power outlet 1,as may be the ±4V of power that such power supplies provide to theirrespective components. Such parasitic coupling will be familiar to thoseskilled in the art. Note also that the particular resistances,capacitances, and voltages described with reference to FIG. 2B arepurely exemplary and may be suitably varied as appropriate to differentconfigurations.

Referring now to FIG. 3A, method 300 of using interface module 110 ofFIGS. 1A-2B during a tissue ablation procedure is described. Theclinician couples the integrated catheter tip (ICT) and indifferentelectrode (IE) to respective I/O ports of the interface module (step301). For example, as shown in FIG. 1A, ICT 122 may be coupled to afirst connector on front panel 111 of interface module 110 via patientinterface module (PIM) 121, and IE 140 may be coupled to a thirdconnector on front panel 111 via indifferent electrode cable 141. Thefirst connector is in operable communication with first I/O port 201(see FIG. 2A) and the third connector is in operable communication withthird I/O port 203 (see FIG. 2A).

In FIG. 3A, the clinician may couple the electrosurgical generator toI/O port(s) of the interface module (step 302). For example, asillustrated in FIG. 1A, electrosurgical generator 130 may be coupled toa second connector on back panel 112 of interface module 110 viaconnection cable 135, and also may be coupled to a fourth connector onback panel 112 via indifferent electrode cable 134. The second connectoris in operable communication with second I/O port 202 (see FIG. 2A), andthe fourth connector is in operable communication with fourth I/O port204 (see FIG. 2A).

In FIG. 3A, the clinician initiates flow of irrigant, positions the ICTwithin the subject, e.g., in the subject's heart, and positions the IEin contact with the subject, e.g., on the subject's back (step 303).Those skilled in the art will be familiar with methods of appropriatelypositioning catheter tips relative to the heart of a subject, forexample via the venous vasculature.

The interface module receives digital radiometer, digital thermocouple,and/or analog ECG signals from the ICT, and receives ablation energyfrom the generator (step 304), for example using the connections, ports,and pathways described above with references to FIGS. 1A-2B. Preferably,the generator may provide such ablation energy to the interface moduleresponsive to the clinician pressing “start” using inputs 133 on thefront face of generator 130 (see FIG. 1A).

The interface module calculates and displays the temperature adjacent tothe ICT, based on the radiometer and thermocouple signals (step 305).This calculation may be performed, for example, by processor 210 basedon instructions in temperature calculation module 233 stored in memory230 (see FIG. 2A). Exemplary methods of performing such a calculationare described in greater detail below with respect to FIG. 3B.

In method 300, the interface module also closes the patient relay so asto provide ablation energy to the ICT for use in tissue ablation (step306). For example, processor 210 may maintain patient relay 250illustrated in FIG. 2A in a normally closed state during operation, suchthat ablation energy flows from electrosurgical generator 130 to ICT 122through interface module 110 without delay upon the clinician'sactuation of the generator, and may open patient relay 250 only upondetection of unsafe conditions such as described below with respect toFIG. 3C. In an alternative embodiment, processor 210 may maintainpatient relay 250 in a normally open state during operation, and maydetermine based on instructions in decision module 234 and on thetemperature calculated in step 305 that it is safe to proceed withtissue ablation, and then close patient relay so as to pass ablationenergy to the ICT. In either case, after a time period defined usinginput 133 on the front face of generator 130, the supply of ablationenergy ceases or the clinician manually turns off the supply of ablationenergy.

The interface module also generates an analog version of thethermocouple signal, and provides the ECG and analog thermocouplesignals to the generator (step 307). Preferably, step 307 is performedcontinuously by the interface module throughout steps 330 through 306,rather than just at the end of the ablation procedure. For example, aswill be familiar to those skilled in the art, the Stockert EP-Shuttle or70 RF Generator may “expect” certain signals to function properly, e.g.,those signals that the generator would receive during a standardablation procedure that did not include use of interface module 110. TheStockert EP-Shuttle or 70 RF generator requires as input an analogthermocouple signal, and optionally may accept analog ECG signal(s). Theinterface module 110 thus may pass through the ECG signal(s) generatedby the ICT to the Stockert EP-shuttle or 70 RF generator via second I/Oport 202. However, as described above with reference to FIGS. 2A and 3A,interface module 110 receives a digital thermocouple signal from ICT122. In its standard configuration, the Stockert EP-Shuttle or 70 RFgenerator is not configured to receive or interpret a digitalthermocouple signal. As such, interface module 110 includes thefunctionality of reconstituting an analog version of the thermocouplesignal, for example using processor 210 and opto-electronics 299, andproviding that analog signal to generator 130 via second I/O port 202.

Turning to FIG. 3B, the steps of method 350 of calculating radiometrictemperature using digital signals from a radiometer and a thermocoupleand operation parameters is described. The steps of the method may beexecuted by processor 210 based on temperature calculation module 233stored in memory 230 (see FIG. 2A). While some of the signals andoperation parameters discussed below are particular to a PIM and ICTconfigured for use with RF ablation energy, other signals and operationparameters may be suitable for use with a PIM and ICT configured for usewith other types of ablation energy. Those skilled in the art will beable to modify the systems and methods provided herein for use withother types of ablation energy.

In FIG. 3B, processor 210 obtains from memory 230 the operationparameters for the thermocouple (TC) and the radiometer (step 351).These operation parameters may include, for example, TCSlope, which isthe slope of the TC response with respect to temperature; TCOffset,which is the offset of the TC response with respect to temperature;RadSlope, which is the slope of the radiometer response with respect totemperature; TrefSlope, which is the slope of a reference temperaturesignal generated by the radiometer with respect to temperature; and F,which is a scaling factor.

Processor 210 then obtains via first I/O port 201 and opto-electronics299 the raw digital signal from the thermocouple, TCRaw (step 352), andcalculates the thermocouple temperature, TCT, based on TCRaw using thefollowing equation (step 353):

${TCT} = {\frac{TCRaw}{TCSlope} - {TCOffset}}$

Next, processor 210 causes temperature display 113 to display TCT untilboth of the following conditions are satisfied: TCT is in the range of35° C. to 39° C., and ablation energy is being provided to the ICT(e.g., until step 306 of FIG. 3A). There are several reasons to displayonly the thermocouple temperature TCT, as opposed to the temperaturecalculated based on signal(s) from the radiometer, until both of theseconditions are satisfied. First, if the temperature TCT measured by thethermocouple is less than 35° C., then based on instructions in decisionmodule 234 the processor 210 interprets that temperature as meaning thatthe ICT is not positioned within a living human body, which would have atemperature of approximately 37° C. If the ICT is not positioned withina living human body, then it would be unsafe to provide power to theradiometer circuitry, as it may rapidly burn out if powered on in air asopposed to blood.

Processor 210 then provides ablation energy to the ICT, e.g., inaccordance with step 306 described above, and receives via second I/Oport 202 two raw digital signals from the radiometer: Vrad, which is avoltage generated by the radiometer based on the temperature adjacentthe ICT; and Vref, which is a reference voltage generated by theradiometer (step 355). Processor 210 calculates the referencetemperature Tref based on Vref using the following equation (step 356):

${Tref} = {\frac{Vref}{TrefSlope} + {TrefOffset}}$

Processor 210 also calculates the radiometric temperature Trad based onVrad and Tref using the following equation (step 357):

${Trad} = {\frac{Vrad}{RadSlope} - {RadOffset} + {Tref}}$

During operation of interface module 110, processor 210 may continuouslycalculate TCT, and also may continuously calculate Tref and Trad duringtimes when ablation power is provided to the ICT (which is subject toseveral conditions discussed further herein). Processor 210 may store inmemory 230 these values at specific times and/or continuously, and usethe stored values to perform further temperature calculations. Forexample, processor 210 may store in memory 230 TCT, Tref, and Trad atbaseline, as the respective values TCBase, TrefBase, and TradBase. Theprocessor then re-calculates the current radiometric temperatureTradCurrent based on the current Vrad received on second I/O port 202,but instead with reference to the baseline reference temperatureTrefBase, using the following equation (step 358):

${TradCurrent} = {\frac{Vrad}{RadSlope} - {RadOffset} + {TrefBase}}$

Processor 210 then calculates and causes temperature display 113 todisplay a scaled radiometric temperature TSrad for use by the clinicianbased on the baseline thermocouple temperature TCBase, the baselineradiometer temperature TradBase, and the current radiometer temperatureTradCurrent, using the following equation (step 359):

TSrad=TCBase+(TradCurrent−TradBase)×F

In this manner, interface module 110 displays for the clinician's use atemperature calculated based on signal(s) from the radiometer that isbased not only on voltages generated by the radiometer and its internalreference, described further below with reference to FIGS. 6A-6B, butalso on temperature measured by the thermocouple.

With respect to FIG. 3C, method 360 of controlling an ablation procedurebased on a temperature calculated based on signal(s) from a radiometer,e.g., as calculated using method 350 of FIG. 3B, and also based onsafety parameters 232 and decision module 234 stored in memory 230 isdescribed.

In FIG. 3C, a slow flow of irrigant is initiated through the ICT and theICT is then positioned within the subject (step 361). For example, inembodiments for use with a Stockert 70 RF Generator, the generator mayautomatically initiate slow irrigant flow to the catheter tip by sendingappropriate signals to a CoolFlow irrigant pumping system associatedwith the generator, responsive to actuation of the generator by theclinician.

Next, the clinician presses a button on the generator to start the flowof ablation energy to the ICT; this may cause the generator to initiatea high flow of irrigant to the ICT and generation of ablation energyfollowing a 5 second delay (step 362). The interface module passes theablation energy to the ICT via the patient relay, as described abovewith respect to step 306 of FIG. 3A.

Based on the calculated and displayed radiometric temperature (seemethods 300 and 350 described above with respect to FIGS. 3A-3B), theclinician determines the temperature of the tissue volume that is beingablated by the ablation energy (step 363). By comparison, temperaturemeasured by a thermocouple alone would provide little to no usefulinformation during this stage of the procedure.

Interface module 110 may use the calculated radiometric temperature todetermine whether the ablation procedure is being performed withinsafety parameters. For example, processor 210 may obtain safetyparameters 232 from memory 230. Among other things, these safetyparameters may include a cutoff temperature above which the ablationprocedure is considered to be “unsafe” because it may result inperforation of the cardiac tissue being ablated, with potentially direconsequences. The cutoff temperature may be any suitable temperaturebelow which one or more unsafe conditions may not occur, for example“popping” such as described below with respect to FIGS. 4C-4D, or tissueburning, but at which the tissue still may be sufficiently heated. Oneexample of a suitable cutoff temperature is 85° C., although higher orlower cutoff temperatures may be used, e.g., 65° C., 70° C., 75° C., 80°C., 90° C., or 95° C. Instructions in decision module 234, also storedin memory 230, cause processor 210 to continuously compare thecalculated radiometric temperature to the cutoff temperature, and if theradiometric temperature exceeds the cutoff temperature, the processormay set an alarm, open the patient relay, and close the load relay so asto return power to the IE via I/O port 204, thereby cutting off flow ofablation energy to the ICT (step 364 of FIG. 3C). Otherwise, theprocessor may allow the ablation procedure to proceed (step 364).

The ablation procedure terminates (step 365), for example, when theclinician presses the appropriate button on generator 130, or when thegenerator 130 automatically cuts of ablation energy at the end of apredetermined period of time.

Referring now to FIGS. 4A-4B, illustrative data obtained during anablation experiment using an interface module constructed in accordancewith the present invention is described. This data was obtained using anunmodified Stockert EP Shuttle Generator with integrated irrigationpump, and a catheter including the PIM 121 and ICT 122 described furtherbelow with reference to FIGS. 5A-6B coupled to interface module 110. TheICT was placed against exposed thigh tissue of a living dog, and theStockert EP Shuttle generator actuated so as to apply 20W of RF energyfor 60 seconds. A Luxtron probe was also inserted at a depth of 3 mminto the dog's thigh. Luxtron probes are considered to provide accuratetemperature information, but are impractical for normal use in cardiacablation procedures because such probes cannot be placed in the heart ofa living being.

FIG. 4A illustrates the change over time in various signals collectedduring the ablation procedure. Signal 410 corresponds to scaledradiometric temperature TSrad; signal 420 corresponds to thethermocouple temperature; signal 430 corresponds to a temperaturemeasured by the Luxtron probe; and signal 440 corresponds to the powergenerated by the Stockert EP Shuttle Generator.

As can be seen from FIG. 4A, power signal 440 indicates that RF powerwas applied to the subject's tissue beginning at a time of about 40seconds and ending at a time of about 100 seconds. Radiometrictemperature signal 410 indicates a sharp rise in temperature beginningat about 40 seconds, from a baseline in region 411 of about 28° C. to amaximum in region 412 of about 67° C., followed by a gradual fall inregion 413 beginning around 100 seconds. The features of radiometrictemperature signal 410 are similar to those of Luxtron probe signal 430,which similarly shows a temperature increase beginning around 40 secondsto a maximum value just before 100 seconds, and then a temperaturedecrease beginning around 100 seconds. This similarity indicates thatthe radiometric temperature has similar accuracy to that of the Luxtronprobe. By comparison, thermocouple signal 420 shows a significantlysmaller temperature increase beginning around 40 seconds, followed by alow-level plateau in the 40-100 second region, and then a decreasebeginning around 100 seconds. The relatively weak response of thethermocouple, and the relatively strong and accurate response of theLuxtron thermocouple, indicate that an unmodified Stockert EP ShuttleGenerator successfully may be retrofit using interface module 110constructed in accordance with the principles of the present inventionto provide a clinician with useful radiometric temperature informationfor use in an ablation procedure.

FIG. 4B illustrates signals obtained during a similar experimentalprocedure, but in which two Luxtron probes were implanted into theanimal's tissue, the first at a depth of 3 mm and the second at a depthof 7 mm. The Stockert EP Shuttle generator was activated, and the RFpower was manually modulated between 5 and 50 W using the power controlknob on the front panel of the generator. In FIG. 4B, the radiometersignal is designated 460, the 3 mm Luxtron designated 470, and the 7 mmLuxtron designated 480. The radiometer and 3 mm Luxtron signals 460, 470may be seen to have relatively similar changes in amplitude to oneanother resulting from the periodic heating of the tissue by RF energy.The 7 mm Luxtron signal 480 may be seen to have a slight periodicity,but far less modulation than do the radiometer and 3 mm Luxtron signals460, 470. This is because the 7 mm Luxtron is sufficiently deep withinthe tissue that ablation energy substantially does not directlypenetrate at that depth. Instead, the tissue at 7 mm may be seen toslowly warm as a function of time, as heat deposited in shallowerportions of the tissue gradually diffuses to a depth of 7 mm.

A series of cardiac ablation procedures were also performed in livinghumans using the experimental setup described above with respect toFIGS. 4A-4B, but omitting the Luxtron probes. The humans all sufferedfrom atrial flutter, were scheduled for conventional cardiac ablationprocedures for the treatment of same, and consented to the clinician'suse of the interface box and ICT during the procedures. The procedureswere performed by a clinician who introduced the ICT into theindividuals' endocardia using conventional methods. During theprocedures, the clinician was not allowed to view the temperaturecalculated by the interface module. As such, the clinician performed theprocedures in the same manner as they would have done with a systemincluding a conventional RF ablation catheter directly connected to aStockert EP-Shuttle generator. The temperature calculated by theinterface module during the various procedures was made available forthe clinician to review at a later time. The clinician performed a totalof 113 ablation procedures on five humans using the above-notedexperimental setup.

FIGS. 4C-4D illustrate data obtained during sequential ablationprocedures performed on a single individual using the experimentalsetup. Specifically, FIG. 4C illustrates the change over time in thesignal 415 corresponding to the scaled radiometric temperature TSrad, aswell as the change over time in the signal 421 corresponding to thethermocouple temperature, during the tenth ablation procedure performedon the individual. During the procedure, about 40 W of RF power wasapplied to the individual's cardiac tissue for 60 seconds (between about20 seconds and 80 seconds in FIG. 4C), and the clinician had a targettemperature 445 of 55° C. to which it was desired to heat the cardiactissue so as to sufficiently interrupt an aberrant pathway causing theindividual's atrial flutter. It can be seen that the scaled radiometrictemperature signal 415, which was subjected to data smoothing in FIG.4C, varied between about 40° C. and 51° C. while RF power was applied.By comparison, as expected, the thermocouple temperature 421 providedessentially no useful information about the tissue temperature duringthe procedure. Notably, the clinician's target temperature 445 of 55° C.was never reached during the procedure, even though the clinicianbelieved based on his or her perceptions of the procedure that suchtemperature had been reached. Because the target temperature 445 was notreached, the tissue was insufficiently heated during the procedure tointerrupt an aberrant pathway. The failure to reach the targettemperature may be attributed to insufficient contact or force betweenthe ablative tip of the ICT and the individual's cardiac tissue, thecondition of the cardiac surface, insufficient power, and the like.

FIG. 4D illustrates the change over time in signal 416 corresponding toTSrad, as well as the change over time in the signal 422 correspondingto the thermocouple temperature, during the eleventh ablation procedureperformed on the same individual as in FIG. 4C. During this procedure,again about 40W of RF power was applied to the individual's cardiactissue for 60 seconds (between about 20 seconds and 80 seconds in FIG.4D), and the clinician again had a target temperature 445 of 55° C. Itcan be seen that the scaled radiometric signal 416, again subject todata smoothing, varied between about 55° C. and 70° C. while RF powerwas applied, while the thermocouple temperature 421 again providedessentially no useful information. Here, the clinician attributed thehigher temperature tissue temperature achieved during the ablation tobetter contact between the ablative tip of the ICT and the individual'scardiac tissue. However, it can be seen that even while RF power wasbeing applied to the tissue, the temperature varied relatively rapidlyover time, e.g., from about 70° C. at about 35 seconds, to about 56° C.at 40 seconds, which may be attributed to variations in the quality ofcontact between the ICT and the individual's cardiac tissue.

The results of the ablation procedures performed on the five individualsare summarized in the following table:

Total % of Total Ablation Number of patients 5 Number of ablations 113Number of ablations that did 50 44% not reach target temperature of 55°C. Number of ablations that 13 12% reached high temperature cutoff of95° C. Number of pops 3  3% Number of successful 5 100%  treatments ofatrial flutter

As can be seen from the above table, 44% of the ablation procedures didnot reach the clinician's target tissue temperature of 55° C. As such,it is likely that this percentage of the procedures resulted ininsufficient tissue heating to interrupt aberrant pathway(s). However,although many of the ablation procedures failed, the clinician repeatedthe ablation procedures a sufficient number of times to achieve 100%treatment of the individuals' atrial flutter. It is believed thatdisplaying the calculated temperature to the clinician during ablationprocedures would enable the clinician to far more accurately assess thequality of contact between the ablative tip of the ICT and theindividual's cardiac tissue, and thus to sufficiently heat the tissueabove the target temperature for a desired period of time, and thusreduce the clinicians' need to repeatedly perform numerous ablationprocedures on the same subject so as to achieve the desired treatment.

As shown in the above table, 12% of the ablation procedures triggeredthe high temperature cutoff such as illustrated in FIG. 3C. Here, thecutoff temperature was defined to be 95° C. However, it was observedthat at this cutoff temperature, “pops” formed during three of theablation procedures. A “pop” occurs when the blood boils because ofexcessive localized heating caused by ablation energy, which results information of a rapidly expanding bubble of hot gas that may causecatastrophic damage to the cardiac tissue. It is believed that a lowercutoff temperature, e.g., 85° C., may inhibit formation of such “pops.”

Additional components that may be used in conjunction with interfacemodule 110 of the present invention, e.g., PIM 121 and ICT 122 ofcatheter 120, are now briefly described with reference to FIGS. 5A-6B.

In FIG. 5A, patient interface module (PIM) 121 that may be associatedwith the integrated catheter tip (ICT) described further below withrespect to FIGS. 6A-6B is described. PIM 121 includes interface moduleconnector 501 that may be connected to front panel 111 of interfacemodule 110, as described with reference to FIG. 1A; PIM circuitry 502,which will be described in greater detail below with reference to FIG.5B; ICT connector 503 that may be connected to catheter 120; and PIMcable 504 that extends between interface module connector 501 and PIMcircuitry 502. PIM 121 is preferably, but not necessarily, designed toremain outside the sterile field during the ablation procedure, andoptionally is reusable with multiple ICT's.

FIG. 5B schematically illustrates internal components of PIM circuitry502, and includes first I/O port 505 configured to be coupled tocatheter 120, e.g., via ICT connector 503, and second I/O port 506configured to be coupled to interface module 110, e.g., via PIM cable504 and interface module connector 501.

PIM circuitry 502 receives on first I/O port 505 an analog thermocouple(TC) signal, raw analog radiometer signals, and analog ECG signals fromcatheter 120. PIM circuitry 502 includes TC signal analog-to-digital(A/D) converter 540 that is configured to convert the analog TC signalto a digital TC signal, and provide the digital TC signal to interfacemodule 110 via second I/O port 506. PIM circuitry 502 includes a seriesof components configured to convert the raw analog radiometer signalsinto a usable digital form. For example, PIM circuitry may includeradiometric signal filter 510 configured to filter residual RF energyfrom the raw analog radiometer signals; radiometric signal decoder 520configured to decode the filtered signals into analog versions of theVref and Vrad signals mentioned above with reference to FIG. 3B; andradiometric signal A/D converter 530 configured to convert the analogVref, Vrad signals into digital Vref, Vrad signals and to provide thosedigital signals to second I/O port for transmission to interface module110. PIM circuitry 502 also passes through the ECG signals to second I/Oport 506 for transmission to interface module 110.

On second I/O port 506, PIM circuitry 502 receives RF ablation energyfrom generator 130 (e.g., a Stockert EP-Shuttle or 70 RF Generator) viainterface module 110. PIM circuitry 502 passes that RF ablation energythrough to catheter 120 via first I/O port 505. PIM circuitry 502 alsoreceives on second I/O port 506 a clock signal generated by RF circuitrywithin interface module 110, as described further above with referenceto FIG. 2B, and passes through the clock signal to first I/O port 505for use in controlling microwave circuitry in ICT 122, as describedbelow.

Referring now to FIGS. 6A-6B, an exemplary integrated catheter tip (ICT)122 for use with the interface module 110 of FIGS. 1A-2B and the PIM ofFIGS. 5A-5B is described. Further detail on components of ICT 122 may befound in U.S. Pat. No. 7,769,469 to Carr, the entire contents of whichare incorporated herein by reference, as well as in U.S. PatentPublication No. 2010/0076424, also to Can (“the Can publication”), theentire contents of which are incorporated herein by reference. Thedevice described in the aforementioned patent and publication do notinclude a thermocouple or ECG electrodes, which preferably are includedin ICT 122 configured for use with interface module 110.

As described in the Can publication and as depicted in FIGS. 6A-6B, ICT122 includes an inner or center conductor 103 supported by a conductivecarrier or insert 104. Carrier 104 may be formed from a cylindricalmetal body having an axial passage 106 that receives conductor 103.Upper and lower sectors of that body extending inward from the ends maybe milled away to expose passage 106 and conductor 103 therein and toform upper and lower substantially parallel flats 108 a and 108 b. Flat108 a may include coplanar rectangular areas 108 aa spaced on oppositesides of conductor 103 near the top thereof. Likewise, flat 108 b mayinclude two coplanar rectangular areas 108 bb spaced on opposite sidesof conductor 103 near the bottom thereof. Thus, carrier 104 may includecenter segment 104 a containing the flats and distal and proximal endsegments 104 b and 104 c, respectively, which remain cylindrical, exceptthat a vertical groove 107 may be formed in proximal segment 104 c.

Center conductor 103 may be fixed coaxially within passage 106 by meansof an electrically insulating collar or bushing 109, e.g. of PTFE, pressfit into passage 106 at distal end segment 104 b of the carrier and by aweld to the passage wall or by an electrically conductive collar orbushing (not shown) at the carrier proximal segment 104 c. This causes ashort circuit between conductor 103 and carrier 104 at the proximal endof the carrier, while an open circuit may be present therebetween at thedistal end of the carrier. In the carrier center segment 104 a, thewalls 106 a of passage 106 may be spaced from center conductor 103. Thisforms a quarter wave stub S, as described in greater detail in U.S. Pat.No. 7,769,469 and U.S. Patent Publication No. 2010/0076424. Conductor103 includes distal end segment 103 a which extends beyond the distalend of carrier 104 a selected distance, and a proximal end segment 103 bwhich extends from the proximal end of ICT 122 and connects to thecenter conductor of cable 105 configured to connect to PIM 121.

As illustrated in FIG. 6B, mounted to the upper and lower flats 108 aand 108 b of carrier 104 is a pair of opposed, parallel, mirror-image,generally rectangular plates 115 a and 115 b. Each plate 115 a, 115 bmay include a thin, e.g. 0.005 in., substrate 116 formed of anelectrically insulating material having a high dielectric constant.Printed, plated or otherwise formed on the opposing or facing surfacesof substrates 116 are axially centered, lengthwise conductive strips117, preferably 0.013-0.016 mm wide, which extend the entire lengths ofsubstrates 116. Also, the opposite or away-facing surfaces of substrates116 are plated with conductive layers 118, e.g. of gold. The side edgesof layers 118 wrap around the side edges of the substrates.

When the ICT is being assembled, plate 115 a may be seated on the upperflat 108 a of carrier 104 and the lower plate 115 b is likewise seatedon the lower flat 108 b so that the center conductor 103 is contactedfrom above and below by the conductive strips 117 of the upper and lowerplates and the layer 118 side edges of those plates contact carriersegment 104 a. A suitable conductive epoxy or cement may be appliedbetween those contacting surfaces to secure the plates in place.

At least one of the plates, e.g. plate 115 a, functions also as asupport surface for one or more monolithic integrated circuit chips(MMICs), e.g. chips 122 and 124. The chip(s) may include a couplingcapacitor connected by a lead (not shown) to center conductor 103 andthe usual components of a radiometer such as a Dicke switch, a noisesource to provide a reference temperature, amplifier stages, a band passfilter to establish the radiometer bandwidth, additional gain stages ifneeded, a detector and buffer amplifier. Due to the relatively smallprofile of the present ICT 122, the above circuit components may bearranged in a string of four chips. The chip(s) may be secured to themetal layer 118 of plate 115 a by a suitable conductive adhesive so thatthat layer which, as described above, is grounded to the insert 104 mayfunction as a ground plane for those chips. The plates also conduct heataway from the chips to conductor 103 and carrier 104. Various leads (notshown) connect the chips to each other and other leads 125 b extendthrough carrier slot 107 and connect the last chip 124 in the string,i.e. the radiometer output, to corresponding conductors of cable 105leading to PIM 121.

A tubular outer conductor 126 may be slid onto carrier 104 from an endthereof so that it snugly engages around the carrier with its proximaland distal ends coinciding with the corresponding ends of the carrier(not shown). The conductor 126 may be fixed in place by a conductiveepoxy or cement applied around the carrier segments 104 b and 104 c.

ICT 122 also may include an annular dielectric spacer 137, e.g. of PTFE,which is centered on the distal end of carrier 104 and surrounds theconductor segment 103 a. The spacer may have a slit 137 a enabling it tobe engaged around that conductor segment from the side thereof. Thespacer 137 may be held in place by a conductive collar 136 whichencircles the spacer and is long enough to slidably engage over a distalend segment of outer conductor 126. The collar 136 may be press fitaround that conductor and carrier segment 104 b to hold it in place andto electrically connect all those elements.

The distal end of the ICT 122 may be closed off by conductive tip 142which, in axial section, may be T shaped. That is, the tip 142 may havediscoid head 142 a that forms the distal end of the ICT and an axiallyextending tubular neck 142 b. The conductor segment 103 a issufficiently long to extend beyond the distal end of the spacer 137 intothe axial passage in neck 104 b. The tip may be secured in place byconductive adhesive applied around the distal end of conductor segment103 a and at the distal end or edge of collar 136. When the tip is inplace, the conductor segment 103 a and tip 104 form a radiometricreceiving antenna, as described in greater detail in U.S. Pat. No.7,769,469 and U.S. Patent Publication No. 2010/0076424.

ICT 122 may further include dielectric sheath 144 which may be engagedover the rear end of outer conductor 126 and slid forwardly until itsdistal end 144 a is spaced a selected distance behind the distal end oftip 142. The conductors 103 and 126 of ICT 122 form an RF transmissionline terminated by the tip 104. When the ICT 122 is operative, thetransmission line may radiate energy for heating tissue only from theuninsulated segment of the probe between tip 104 and the distal end 144a of the sheath 144. That segment thus constitutes an RF ablationantenna.

The proximal ends of the center conductor segment 103 b, outer conductor126 and sheath 144 may be connected, respectively, to the inner andouter conductors and outer sheath of cable 105 that leads to PIM 121.Alternatively, those elements may be extensions of the correspondingcomponents of cable 105. In any event, that cable 105 connects thecenter conductor 103 to the output of a transmitter which transmits a RFheating signal at a selected heating frequency, e.g. 500 GHz, to the RFablation antenna.

As illustrated in FIG. 6A, ICT 122 further may include first, second,and third ECG electrodes 190 disposed on the outside of sheath 144, aswell as a thermocouple 191 positioned so as to detect the temperature ofblood or tissue in contact with ICT 122. Signals generated by electrodes190 and thermocouple 191 may be provided along cable 105 connected toPIM 121.

If desired, cable 105 further may include probe steering wire 145 whoseleading end 145 a may be secured to the wall of a passage 146 in carriersegment 104 c.

Preferably, helical through slot 147 is provided in collar 136 as shownin FIGS. 6A-6B. The collar material left between the slot turnsessentially forms helical wire 148 that bridges spacer 137. Wire 148 isfound to improve the microwave antenna pattern of the radiometricreceiving antenna without materially degrading the RF heating pattern ofthe RF ablation antenna.

The inner or center conductor 103 may be a solid wire, or preferably isformed as a tube that enables conductor 103 to carry an irrigation fluidor coolant to the interior of probe tip 142 for distribution therefromthrough radial passages 155 in tip head 142 a that communicate with thedistal end of the axial passage in tip neck 142 b.

When plates 115 a and 115 b are seated on and secured to the upper andlower flats 108 a and 108 b, respectively, of carrier 104, conductivestrips 117, 117 of those members may be electrically connected to centerconductor 103 at the top and bottom thereof so that conductor 103 formsthe center conducts for of a slab-type transmission line whose groundplane includes layers 118, 118.

When ablation energy is provided to ICT 122, a microwave field existswithin the substrate 116 and is concentrated between the centerconductor 103 and layers 118, 118. Preferably, as noted here, conductiveepoxy is applied between conductor 103 and strips 117 to ensure that noair gaps exist there because such a gap would have a significant effecton the impedance of the transmission line as the highest field parts areclosest to conductor 103.

Plates 115 a, 115 b and conductor 103 segment together with carrier 104form a quarter wave (λ_(R)/4) stub S that may be tuned to the frequencyof radiometer circuit 124, e.g. 4 GHz. The quarter wave stub S may betuned to the center frequency of the radiometer circuit along withcomponents in chips 122, 124 to form a low pass filter in the signaltransmitting path to the RF ablation antenna, while other components ofthe chips form a high pass or band pass filter in the signal receivingpath from the antenna to the radiometer. The combination forms a passivediplexer D which prevents the lower frequency transmitter signals on thesignal transmitting path from antenna T from reaching the radiometer,while isolating the path to the transmitter from the higher frequencysignals on the signal receiving path from the antenna.

The impedance of the quarter wave stub S depends upon the K value andthickness t of substrates 116 of the two plates 115 a, 115 b and thespacing of center conductor 103 from the walls 106 a, 106 a of passage106 in the carrier center segment 104 a. Because the center conductor103 is not surrounded by a ceramic sleeve, those walls can be movedcloser to the center conductor, enabling accurate tuning of thesuspended substrate transmission line impedance while minimizing theoverall diameter of the ICT 122. As noted above, the length of the stubS may also be reduced by making substrate 116 of a dielectric materialwhich has a relatively high K value.

In one working embodiment of the ICT 122, which is only about 0.43 in.long and about 0.08 in. in diameter, the components of the ICT have thefollowing dimensions:

Component Dimension (inches) Conductor 103 0.020 outer diameter 0.016inner diameter (if hollow) Substrate 116 (K = 9.8) 0.065 wide; thicknesst = 0.005 Strips 117 0.015 wide Air gap between 103 and each 106a 0.015

Thus, the overall length and diameter of the ICT 122 may be relativelysmall, which is a useful feature for devices configured for percutaneoususe.

While various illustrative embodiments of the invention are describedabove, it will be apparent to one skilled in the art that variouschanges and modifications may be made herein without departing from theinvention. For example, although the interface module has primarily beendescribed with reference for use with an RF electrosurgical generatorand the PIM and ICT illustrated in FIGS. 5A-6B, it should be understoodthat the interface module suitably may be adapted for use with othersources of ablation energy and other types of radiometers. Moreover, theradiometer may have components in the ICT and/or the PIM, and need notnecessarily be located entirely in the ICT. Furthermore, thefunctionality of the radiometer, ICT, and/or PIM optionally may beincluded in the interface module. The appended claims are intended tocover all such changes and modifications that fall within the truespirit and scope of the invention.

What is claimed:
 1. An interface module for use with an ablation energygenerator and an integrated catheter tip (ICT), the ICT including aradiometer, an ablative tip, and a thermocouple, the interface modulecomprising: a processor; a first input/output (I/O) port configured toreceive a digital radiometer signal and a digital thermocouple signalfrom the ICT; a second I/O port configured to receive ablative energyfrom the ablation energy generator; a temperature display; a patientrelay in communication with the first I/O port, the second I/O port, andthe processor; a non-transitory computer-readable medium storingoperation parameters for the radiometer and for the thermocouple, andfurther storing instructions for causing the processor to execute thesteps of: (a) calculating a temperature adjacent to the ICT based on thedigital radiometer signal, the digital thermocouple signal, and theoperation parameters; (b) causing the temperature display to display thecalculated temperature; and (c) closing the patient relay such that thepatient relay passes ablative energy received on the second I/O port tothe first I/O port.
 2. The interface module of claim 1, furthercomprising a load relay and a dummy load, and wherein thecomputer-readable medium further stores a safety cutoff temperature andinstructions for causing the processor to execute the steps of (d)comparing the calculated temperature to the safety cutoff temperaturewhile the patient relay is closed; and (e) if the calculated temperatureexceeds the safety cutoff temperature, opening the patient relay andclosing the load relay such that the load relay passes ablative energyreceived on the second I/O port to the dummy load.
 3. The interfacemodule of claim 1, wherein the instructions cause the processor tomaintain the patient relay in a normally closed state and to open thepatient relay upon detection of an unsafe condition.
 4. The interfacemodule of claim 1, wherein the computer-readable medium further storesinstructions for causing the processor to execute the steps of: (d)initially calculating a temperature adjacent to the ICT based on thedigital thermocouple and the operation parameters but not the digitalradiometer signal; (e) causing the temperature display to display theinitially calculated temperature; and (f) if the temperature calculatedin step (d) is in the range of 35° C. to 39° C. and if the second I/Oport is receiving ablative energy from the ablation energy generator,then executing steps (a)-(c).
 5. The interface module of claim 1,wherein the operation parameters comprise a slope and offset describinga temperature response of the radiometer, and further comprise a slopeand offset describing a temperature response of the thermocouple.
 6. Theinterface module of claim 1, wherein the computer-readable mediumfurther stores instructions for causing the processor to execute thesteps of: generating an analog thermocouple signal based on the digitalthermocouple signal; and providing the analog thermocouple signal to thesecond I/O port for transmission to the ablation energy generator. 7.The interface module of claim 1, wherein the ICT further includes ECGelectrodes, wherein the first I/O port is configured to receive ECGsignals generated by the ECG electrodes from the ICT, and wherein thesecond I/O port is configured to provide the ECG signals to the ablationenergy generator.
 8. The interface module of claim 1, further comprisinga third I/O port configured to receive a signal from an indifferentelectrode and a fourth I/O port configured to provide the signal fromthe indifferent electrode to the ablation energy generator.
 9. Theinterface module of claim 1, wherein the ablative energy is selectedfrom the group consisting of RF energy, microwave energy, cryoablationenergy, and high frequency ultrasound energy.
 10. The interface moduleof claim 1, wherein the ablative energy is RF energy.
 11. A method ofusing an interface module with an ablation energy generator and anintegrated catheter tip (ICT), the ICT including a radiometer, anablative tip, and a thermocouple, the method of using the interfacemodule comprising the steps of: (a) receiving at a first I/O port of theinterface module a digital radiometer signal and a digital thermocouplesignal from the ICT; (b) receiving at a second I/O port of the interfacemodule ablative energy from the ablation energy generator; (c)calculating at the interface module a temperature adjacent to the ICTbased on the digital radiometer signal, the digital thermocouple signal,and the operation parameters; (d) displaying on a temperature display ofthe interface module the calculated temperature; and (e) passingablative energy received on the second I/O port to the first I/O port byclosing a patient relay of the ablation module.
 12. The method of claim11, further comprising the steps of: (f) storing at the interface modulea safety cutoff temperature; (g) at the interface module, comparing thecalculated temperature to the safety cutoff temperature while thepatient relay is closed; and (h) if the calculated temperature exceedsthe safety cutoff temperature, opening the patient relay and closing aload relay of the ablation module such that the load relay passesablative energy received on the second I/O port to a dummy load of theablation module.
 13. The method of claim 11, wherein the patient relayis maintained in a normally closed state and opened upon detection of anunsafe condition.
 14. The method of claim 11, further comprising thesteps of: (f) initially calculating at the interface module atemperature adjacent to the ICT based on the digital thermocouple andthe operation parameters but not the digital radiometer signal; (g)displaying on the temperature display the initially calculatedtemperature; and (h) if the temperature calculated in step (f) is in therange of 35° C. to 39° C. and if the second I/O port is receivingablative energy from the ablation energy generator, then performingsteps (c)-(e).
 15. The method of claim 11, wherein the operationparameters comprise a slope and offset describing a temperature responseof the radiometer, and further comprise a slope and offset describing atemperature response of the thermocouple.
 16. The method of claim 11,further comprising the steps of: (f) generating at the interface modulean analog thermocouple signal based on the digital thermocouple signal;and (g) providing the analog thermocouple signal to the second I/O portfor transmission to the ablation energy generator.
 17. The method ofclaim 11, wherein the ICT further includes ECG electrodes, the methodfurther comprising the steps of: (f) receiving at the first I/O port ECGsignals generated by the ECG electrodes from the ICT, and (g) providingat the second I/O port the ECG signals to the ablation energy generator.18. The method of claim 11, further comprising the steps of: (f)receiving at a third I/O port of the ablation energy generator a signalfrom an indifferent electrode; and (g) providing at a fourth I/O portthe signal from the indifferent electrode to the ablation energygenerator.
 19. The method of claim 11, wherein the ablative energy isselected from the group consisting of RF energy, microwave energy,cryoablation energy, and high frequency ultrasound energy.
 20. Themethod of claim 11, wherein the ablative energy is RF energy.